Scintillation and Semiconductor Detectors

Abstract

As stated in Chapter 7, the detection efficiency of γ- and x-rays in gas detectors is very low, because these penetrating radiations travel through the low-density gas with little interaction. To improve counting efficiency for these radiations, solid and liquid scintillation detectors with high density are used. These detectors have the unique property of emitting scintillations or flashes of light after absorbing γ- or x-radiations. The γ- or x-rays interact with scintillation detectors via photoelectric, Compton, and/or pair production mechanisms, whereby the detector molecules are raised to higher energy states through ionization or excitation. These high-energy states return to ground states by emitting light photons.The time to reach the ground state is called the scintillation decay time. The light photons produced are converted to an electrical pulse by means of a photomultiplier (PM) tube (described later). The pulse is then amplified by a linear amplifier, sorted by a pulse-height analyzer (PHA), and then registered as a count. Different solid or liquid detectors are used for different types of radiation. For example, sodium iodide detectors containing a trace of thallium (NaI[Tl]) are used for γ- and x-ray detection, whereas organic detectors such as anthracene and plastic fluors are used for β ⁻ particle detection.